The present invention relates to a method of reinforcing a stratified composite material part comprising at least one through-hole, as well as a reinforced stratified composite material part.
Stratified composite materials are widely used in the aeronautical field, particularly on account of their mechanical resistance and high specific modulus of elasticity.
A stratified composite material part comprises a stack of fiber layers which are embedded in a resin matrix.
In most cases, as illustrated in FIGS. 1 and 2, a stratified composite material part 10 is connected to other parts 12 by means of at least one fastening 14, such as a bolt or a rivet, for example, and comprises at least one through-hole 16 to partially accommodate the fastening 14. Said fastening makes it possible to guarantee not only the connection between the parts 10 and 12, but likewise the transmission of forces between them. Depending on the forces transmitted, a flow of more or less significant stresses passes along the edge of the hole.
The stress concentration zones, such as a hole for example, are sensitive zones for the composite material parts, as stress concentrations are zones that are susceptible the appearance of premature damage to the composite material. As a result, one or a plurality of cracks 18, loss of fiber/matrix cohesion, delamination may appear from the hole.
In the case of a composite material, the machining of a hole results in the fibers being cut, which necessarily alters the mechanical characteristics of the part, but likewise generates faults such as micro-cracks at the wall of the hole, for example.
In the case of a composite material, in the absence of significant plastic deformation, the single point stress of a fault (such as a micro-crack) grows very significantly until the composite ruptures.
In order to improve the mechanical performance of a composite material part, a solution involves increasing the thickness of the part at the level of the holes, so as to increase the size of the working section. However, this solution leads to an increase in the weight of the part and therefore the total weight of the aircraft. Moreover, this local increase in the thickness of the part about the holes may make the shaping of the part more complex and therefore increase its cost.
Another solution involves disposing an insert in the form of a tube in the hole to improve the transmission of stress flows. However, this solution makes the manufacturing process more complex and therefore increases the cost of the part.
Other solutions aimed at improving the quality of the drilling have been developed, in order to reduce the risks of an incipient break. Even if these solutions allow the characteristics of the composite material part to be improved, they lead to an increase in the cost of the part.